Organic No-till Production in Iowa: Effects On Crop Productivity and Soil Quality.

A multi-state, long-term organic experiment was established in six states in 2008 as a comprehensive examination of the effects of organic no-till production on crop productivity, yields, soil quality, and economic performance. Following wheat harvest in the first year, cover crops were seeded at all sites in September 2008 to prepare for the initiation of the no-till segment of the study. Tillage treatments included conventional tillage (CT) and no-till (NT), with cover crop planted in the future NT plots as either hairy vetch (HV) or rye. Grain crops planted the following spring were corn (following HV) and soybean (following rye) in 2009 and again in 2011. In May to June (weather-dependent), cover crops were either disked in the conventional till treatment (CT) or rolled/crimped in the organic no-till system (NT) with the goal of the crushed cover crops serving as a dried mulch between corn and soybean rows throughout the season. Treatments were arranged in a randomized complete block design as a 2 x 2 factorial with treatment combinations replicated four times. Oats were planted in all plots in 2010, to create a three-crop rotation in each system. Results from the Iowa site showed that corn and soybean plant populations were similar between treatments both years; and NT soybean yields (averaging 2.62 Mg/ha) were equivalent to CT organic soybeans (2.89 Mg/ha) in 2009, and in 2011, in a wetter, cooler year, NT soybeans averaged 2.08 Mg/ha compared to 1.88 Mg/ha in CT. No-till organic corn, which suffered from winter kill of HV and insufficient HV biomass, extensive early rains, failure of vetch termination, excessive weeds, and lack of N from cover crops alone, averaged 1.82 Mg/ha compared to the tilled organic corn averaging 6.20 Mg/ha in 2009. Perennial weeds, such as Canada thistle, dandelion, quackgrass and clovers, and resurgence of previously planted HV, challenged NT plots over time. Annual and perennial grass weeds were lower than broadleaf weed populations, with a CT/NT ratio of 1/1-to-3/1, suggesting oat, corn and soybeans are reasonably competitive with grass weeds in the NT system. Soil quality analysis in Fall 2008 revealed no significant differences in any parameters between the NT and the CT treatments but after the first corn and soybean season in Fall 2009, soil microbial biomass carbon (MBC) values were significantly greater in NT than in CT plots in Fall 2009, and at the end of the second season following oats (2010), residual soil nitrate-N, pH and electrical conductivity were greater under NT than CT and bulk density was significantly lower under NT. Although MBC was not significantly different in NT vs. CT in Fall 2010, NT MBC was numerically higher than CT MBC (NT–194 vs. CT–185 mg/g).  Microbial biomass nitrogen (MBN) followed a similar trend with significantly greater MBN in organic NT over CT: NT–48 vs. CT–35 mg/g. In Fall 2011, nitrogen mineralization potential and soil pH were significantly greater in organic NT soil compared to CT soil, and bulk density was significantly lower in NT soil. Results of this study demonstrate that the soil microbial community responds quickly to changes in soil management, in this case, reduced soil disturbance and increased surface residue cover under NT. Lower bulk density of NT surface soil results in greater porosity which can enhance microbial habitat through increased water-filled pore space. Our findings also show that within 3 years, organic NT management resulted in higher nitrogen mineralization potential, reflecting the soil’s ability to release N from labile organic N pools and improved fertility. We plan to continue this long-term experiment to verify long-term changes induced by the different soil management strategies (i.e., NT and CT). An economic and energy analysis will examine the benefits of organic NT in terms of carbon-offset programs and explore the possibilities of specific phases (i.e., oats and alfalfa) for pasture integration.